1. Field of the Invention
The present invention relates to a method of producing a catalytic converter, particularly the method of producing the catalytic converter with a catalyst substrate held in a cylindrical housing through a shock absorbent member.
2. Description of the Related Arts
In order to produce catalytic converters mounted on recent vehicles, generally employed is such a method for rolling a ceramic mat around a catalyst substrate to form a shock absorbent member, and pressing the shock absorbent mat into a casing, or cylindrical housing. On one hand, the shock absorbent mat is required to be made thick and soft to provide its shock absorbing function, on the other hand, the shock absorbent mat is required to be made thin and hard to press it into the casing easily. In order to meet those requirements contradictory to each other, the shock absorbent mat has to be made to reach a compromise between them.
According to the prior method, therefore, it has been pointed out that the catalyst substrate could not be protected by the shock absorbent mat sufficiently, to deteriorate the substrate, or that the catalyst substrate and the shock absorbent mat were damaged when they were pressed into the casing. In order to solve those problems, it has been proposed that after the catalyst substrate and the shock absorbent mat were inserted into the cylindrical housing, the housing is compressed so as to compress the shock absorbent mat by a certain amount, as disclosed in publications such as U.S. Pat. No. 5,329,698, Japanese Patent Laid-open Publication Nos. 64-60711, 9-234377, 9-170424 and so on.
With respect to the cylindrical housing for holding the catalyst substrate therein, it has been proposed in Japanese Utility-model Laid-open Publication No. 61-110823 that in order to overcome inconvenience in a prior method for welding a casing body with cone portions at its opposite ends, a tubular member or pipe is increased or decreased in diameter to form the casing body and at least one of the cone portions in a body, thereby to produce a case for holding the catalyst substrate. In this Publication, it is disclosed that one end portion of the tubular member having the same diameter with that of the casing body is reduced in diameter to form a cone portion and a guide pipe integrally, and the catalyst substrate and cushion member are inserted into a cylindrical portion of the casing body, and then an open end portion of the case except for the casing body is reduced in diameter by a spinning process to integrate it with the other cone portion and the guide pipe. However, the Publication is silent about the spinning process, nor a possibility for applying the spinning process to the casing body.
Also, Japanese Patent Laid-open Publication No. 9-112259 discloses a prior method of producing a monolithic catalyst converter by welding flanges of an upper member and a lower member, with a monolithic catalyst held between the upper member and lower member, and another prior method for welding a cylindrical portion with cone portions at its opposite ends. In order to overcome inconvenience in assembling parts according to the prior methods, the Publication proposes such a method of producing a monolithic catalyst converter that has an inserting process for inserting the monolithic catalyst into a cylindrical pipe member, and a drawing process for drawing opposite open ends of the pipe member to form them into a funnel shape respectively. It is disclosed in the publication that the drawing process is performed by a drawing apparatus with dies, or a spinning drawing apparatus, which is shown in FIG. 9 of the Publication, and which is explained that a roller is pressed onto one opening end of the pipe member, with the pipe member being rotated about its axis. In FIG. 5 of the Publication, there is disclosed such a method that after the process for inserting the monolithic catalyst and the drawing process were performed, a pressing jig having rollers is pressed onto the pipe member to form ring-shaped recesses on its cylindrical portion.
In the methods of producing the catalytic converters as disclosed in the above-described Japanese Publication Nos. 61-110823 and 9-112259, the drawing process is performed by the spinning process, which has not been explained practically in the Publication No. 61-110823, but which has been disclosed in FIG. 9 of the Publication No. 9-112259. That is, it is apparent from the Publication No. 9-112259 that the spinning process is a known process, in which a single roller is pressed onto one opening end of the pipe member, with the pipe member being rotated about its axis, and which had been generally used as an embodiment of the drawing process. Otherwise, any process different from the general process should have been explained in the Publications. For example, Japanese Patent Laid-open Publication No. 3-146232, which relates to a technical field entirely different from the catalytic converter, discloses a method for processing an end portion of a tubular member having grooves formed therein, wherein a forming roll is pressed onto an end portion of a grooved pipe material formed inside surface thereof with grooves in the longitudinal direction, and rotated by a rotating mechanism, and the end portion of the tubular member is drawn to be decreased in diameter, with the forming roll revolved and freely rotated in accordance with rotation of the rotating mechanism, and moved in a radial direction. In that method, the single forming roll has been employed, as in the prior method.
According to the method for holding the catalyst substrate in the cylindrical housing through the shock absorbent member as disclosed in the aforementioned Publication, the compressing process by means of the die, or the compressing process by means of the pressing jig has been employed, so that the workpiece of the cylindrical housing is formed only by the compressing force in the circumferential direction or radial direction. Therefore, the material of the workpiece will be hardly moved in the circumferential direction and radial direction, to cause a buckling of the workpiece, or an uneven wall thickness of the cylindrical housing, which will possibly result in uneven compressed amount of the shock absorbent mat, and consequently uneven force for holding the catalyst substrate. Thus, the prior method can not be the best method. While it may not cause the buckling of the workpiece, nor uneven wall thickness of the cylindrical housing, it is very difficult for the prior method to obtain a circularity of the cylindrical housing, and provide evenly compressed amount of the shock absorbent mat around the whole circumference. In view of those circumstances, such a method as compressing the shock absorbent mat evenly and accurately in its longitudinal direction around its whole circumference has been desired.
Accordingly, it is an object of the present invention to provide a method of producing a catalytic converter with a catalyst substrate held in a cylindrical housing through a shock absorbent member, by reducing the cylindrical housing and shock absorbent member in diameter evenly, to hold the catalyst substrate properly.
In accomplishing the above and other objects, the method of producing the catalytic converter may comprise providing a shock absorbent member around an outer periphery of a catalyst substrate, inserting the catalyst substrate and the shock absorbent member into a cylindrical workpiece, fixing the cylindrical workpiece to prevent the cylindrical workpiece from being rotated about a longitudinal axis thereof, and spinning at least a portion of the cylindrical workpiece covering at least a portion of the shock absorbent member, by means of a plurality of spinning rollers, which are evenly positioned around the outer periphery of the cylindrical workpiece, and which are revolved about the axis of the cylindrical workpiece along a common circular locus, and moved in a radial direction of the cylindrical workpiece, to reduce the cylindrical workpiece and the shock absorbent member in diameter, and hold the catalyst substrate in the cylindrical workpiece.
The method may further comprise measuring an outer diameter of the catalyst substrate and an inner diameter of the cylindrical workpiece, calculating a target amount of the shock absorbent member to be reduced on the basis of the measured diameters, and moving the spinning rollers in the radial direction of the cylindrical workpiece by the target amount to be reduced.
The method may further comprise reducing the diameter of the portion of the cylindrical workpiece covering the portion of the shock absorbent member by the spinning rollers, and simultaneously applying a necking process to at least one end portion of the cylindrical workpiece by the spinning rollers, to form a neck portion of the cylindrical workpiece.
The spinning process may be applied to the portion of the cylindrical workpiece covering the portion of the shock absorbent member, with opposite ends of the cylindrical workpiece securely fixed, to reduce the diameter of the cylindrical workpiece together with the shock absorbent member, and hold the catalyst substrate in the cylindrical workpiece.